Space and velocity distributions of Galactic isolated old Neutron stars

TL;DR

This paper uses Monte-Carlo simulations to model the current space and velocity distributions of Galactic isolated old neutron stars, considering different formation scenarios and initial velocity distributions.

Contribution

It provides a comprehensive simulation-based catalogue of neutron star positions and velocities, accounting for various formation histories and initial velocity models.

Findings

NS density in solar neighborhood: 2-4x10^-4 pc^-3

NS scale height: 0.3-0.6 kpc

Negligible effect of Galactic dynamical heating on NS distributions

Abstract

I present the results of Monte-Carlo orbital simulations of Galactic Neutron Stars (NSs). The simulations take into account the up-to-date observed NS space and velocity distributions at birth, and account for their formation rate. I simulate two populations of NSs. Objects in the first population were born in the Galactic disk at a constant rate, in the past 12 Gyr. Those in the second population were formed simultaneously 12 Gyr ago in the Galactic bulge. I assume that the NSs born in the Galactic disk comprise 40% of the total NS population. Since the initial velocity distribution of NSs is not well known, I run two sets of simulations, each containing 3x10^6 simulated NSs. One set utilizes a bimodal initial velocity distribution and the other a unimodal initial velocity distribution, both are advocated based on pulsars observations. In light of recent observational results, I discuss the effect of dynamical heating by Galactic structure on NS space and velocity distributions and show it can be neglected. I present catalogue of simulated NS space and velocity vectors in the current epoch, and catalogue of positions, distances and proper motions of simulated NSs, relative to the Sun. Assuming there are 10^9 NSs in the Galaxy, I find that in the solar neighborhood the density of NSs is about 2-4x10^-4 pc^-3 and their scale height is about 0.3-0.6 kpc (depending on the adopted initial velocity distribution). These catalogue can be used to test the hypothesis that some radio transients are related to these objects.